Method for temperature compensation of an image dectector

ABSTRACT

This is a method for temperature compensation of an image detector comprising photosensitive spots (O 1  to O 6,  R 1  to R 9 ), these being sensitive to ambient temperature, each connected to a row conductor (Y 1  to Y 3 ) and a column conductor (W 1,  W 2,  Z 1  to Z 3 ). Each of the photosensitive spots is connected via one of its conductors to a read circuit ( 30   a   , 30   b ). The photosensitive spots are divided into detecting photosensitive spots (R 1  to R 9 ), intended to be exposed to light information corresponding to the image to be detected, the read circuits ( 30   b ) associated with these photosensitive spots each delivering a measurement voltage representative of the image to be detected, and into blind photosensitive spots (O 1  to O 6 ) protected from the light information, the read circuits ( 30   a ) associated with these blind photosensitive spots each delivering a dark voltage serving for temperature compensation. During detection of an image, the method consists in picking up the dark voltages, then in generating an average correction value from the dark voltages coming from one or more detected images and in using the average correction value to generate a correction voltage (VDR) to be applied, during detection of a subsequent image, to the read circuits ( 30   b ) associated with the detecting photosensitive spots (R 1  to R 9 ) so that they deliver a measurement voltage made substantially independent of temperature.  
     Application in particular to radiological image detectors.

[0001] The present invention relates to a method of temperaturecompensation of an image detector, which makes it virtually insensitiveto temperature fluctuations and which in particular guarantees that ithas an approximately constant image dynamic range whatever thetemperature.

[0002] In this type of image detector, the acquisition of an image takesplace with the aid of one or more photosensitive spots each formed froma photodiode and a switch. The photosensitive spots are produced withthe aid of techniques for the thin-film deposition of semiconductormaterials such as hydrogenated amorphous silicon (aSiH). Thesephotosensitive spots, arranged in the form of a matrix or linear array,make it possible to detect images contained within visible ornear-visible radiation. The signals that are produced by said spots arethen generally digitized so as to be able to be stored and processedeasily.

[0003] These arrangements of photosensitive spots find one particularlyadvantageous application in the medical field or the field of industrialinspection, in which they detect radiological images. All that isrequired is to cover them with a scintillator and to expose the latterto X-radiation carrying a radiological image. The scintillator convertsthe incident X-radiation into radiation in the band of wavelengths towhich the photosensitive spots are sensitive.

[0004] There are now large photosensitive matrices which may haveseveral million photosensitive spots.

[0005]FIG. 1 shows a matrix image detector of known type. It has onlynine photosensitive spots in order not to unnecessarily clutter up thefigure. Each photosensitive spot P1 to P9 is formed from a photodiode Dpand an element having a switch function Dc represented in the form of aswitching diode. It would have been possible to choose a transistor aselement having a switching function. The photodiode Dp and the switchingdiode Dc are connected together in a back-to-back arrangement.

[0006] Each photosensitive spot P1 to P9 is connected between a rowconductor Y1 to Y3 and a column conductor X1 to X3. The row conductorsY1 to Y3 are connected to an addressing device 3 known as a driver.There may be several drivers 3 if the matrix is of large size. Theaddressing device 3 generally comprises shift registers, switchingcircuits and clock circuits. The addressing device 3 raises the rowconductors Y1 to Y3 to voltages which either isolate the photosensitivespots P1 to P3 connected to the same row conductor Y1 from the rest ofthe matrix or turn them on. The addressing device 3 allows the rowconductors Y1 to Y3 to be addressed sequentially.

[0007] The column conductors X1 to X3 are connected to a read device CL.

[0008] During an image record phase, during which the photosensitivespots P1 to P9 are exposed to a signal to be picked up and are in areceiving state, that is to say their reverse-biased photosensitivediodes Dp and switching diodes Dc each constitute a capacitor, there isa build up of charges at the junction point A between the two diodes Dp,Dc. The amount of charge is approximately proportional to the intensityof the signal received, whether this is very intense illumination,provided that the photosensitive diodes remain in the linear detectionrange, or darkness. There then follows a read phase, during which a readpulse is sequentially applied to the row conductors Y1 to Y3, which readpulse turns on the photodiodes Dp and makes it possible for the chargesaccumulated in the column conductors X1 to X3 to drain away to the readdevice CL.

[0009] The read device CL will now be explained in greater detail. Itconsists of as many read circuits as there are column conductors X1 toX3 and these read circuits are of the charge-integrating circuit type 5.Each charge-integrating circuit is formed by an operational amplifier G1to G3 mounted as an integrator by means of a read capacitor C1 to C3.Each capacitor is mounted between the negative input of the operationalamplifier G1 to G3 and its output S1 to S3. Each column conductor X1 toX3 is connected to the negative input of an operational amplifier G1 toG3. The positive input of each of the operational amplifiers, G1 to G3is taken to a constant input reference voltage VR, which sets thisreference voltage on each column conductor X1 to X3. Each operationalamplifier G1 to G3 comprises a resetting switch I1 to I3 mounted inparallel with the capacitor C1 to C3.

[0010] The outputs S1 to S3 of the integrating circuits are connected toa multiplexing device 6 which delivers, as a series, signalscorresponding to the charges which were integrated by thecharge-integrating circuits. In the read phase, these signals correspondto the charges accumulated by all the photosensitive spots of the samerow. The signals delivered by the multiplexing device 6 are thendigitized in at least one analog-to-digital converter 7, the digitizedsignals output by the analog-to-digital converter 7 translating thecontent of image to be detected. These digitized signals are sent to amanagement system 8 which can store, process and display them.

[0011] Defects affect the quality of the useful images from suchphotosensitive devices.

[0012] The semiconductor components of the photosensitive spots exhibitremanence which is associated especially with their imperfectcrystalline structure. Charges corresponding to an image record phaseare not read during the associated read phase and are reproduced duringthe read phase for a subsequent image. To try to overcome remanenceproblems, it has been proposed, especially in patent applicationEP-A-364 314, to add to the charge due to the signal to be picked up adrive charge and to apply, between two read pulses, a bias pulse whoseamplitude is generally less than that of the read pulse.

[0013] The semiconductor components of the photosensitive spots are notall exactly identical and the matrix of photosensitive spots has locallyimpaired regions. The components of the read device CL also contributeinhomogeneities.

[0014] It is common practice to correct the useful image with what iscalled an offset image, also known as a “black image”. This black imageis made at the start of the operating cycle by exposing the imagedetector, during the image record phase, to a signal of zero intensity,and then carrying out the read phase.

[0015] The offset image is produced in the absence of any illuminationand the charges read, at the photosensitive spot, during thecorresponding read phase, fall within the following three categories.The first represents the drive charges, the value of which is given by:

Q=(VP2−VP1)Cp

[0016] with:

[0017] VP2, the amplitude of the read pulse;

[0018] VP1, the amplitude of the bias pulse (these read and bias pulsesare delivered by the addressing circuit 3); and

[0019] Cp, the capacitance of the photosensitive spot P1 to P9.

[0020] The second category of charges corresponds to the charges arisingfrom the leakage current of the photodiode Dp of the photosensitive spotread, this current being established between the application of twosuccessive read pulses or bias pulses.

[0021] The third category of charges corresponds to the charges arisingfrom the leakage current emanating from all the photosensitive spotsconnected to the same column conductor as that which is read, but onlyduring the read phase.

[0022] However, it has turned out that although the first category ofcharges is relatively temperature-stable, the same does not apply in thecase of the other two categories of charges. The offset image varieswith temperature. This variation may be very significant, for example at25° C., the electric charge, accumulated at a photosensitive spot of theoffset image and converted into a voltage by the charge-integratingcircuit 5, may be 0.5 volts, while it may reach up to 2 volts at 50° C.

[0023] This phenomenon is annoying; it may be overcome, but in arestricting manner, by recording offset images often and by correctingthe useful image with these offset images, at a sufficiently highfrequency compared with the thermal time constants of the photosensitivedevice.

[0024] In addition, it turns out that this phenomenon causes otherdrawbacks, the more one works at high temperature. The dynamic range ofthe image detector degrades with temperature. The images that itproduces become less and less well contrasted as the temperatureincreases and fewer and fewer shades can be rendered. The dynamic rangeof the image is degraded.

[0025] This is because the analog-to-digital converter 7 has a fixedencoding range for digitizing the voltage values delivered by themultiplexing device 6 for each of the photosensitive spots. A typicalvalue of the encoding range is between 0 volts and 5 volts. If, at 40°C., the level of the offset of a photosensitive spot is 1.8 volts, thereremains only 3.2 volts available for encoding the level of thisphotosensitive spot in the useful image.

[0026] The present invention aims to overcome the abovementionedproblems associated with the variations in ambient temperature andprovides a method for temperature compensation of an image detectormaking it virtually insensitive to the inevitable fluctuations inambient temperature.

[0027] To achieve this, the method according to the invention is amethod for temperature compensation of an image detector comprisingphotosensitive spots, these being sensitive to ambient temperature, eachconnected to a row conductor and a column conductor, each of thephotosensitive spots being connected via one of its conductors to a readcircuit. The photosensitive spots are divided into detectingphotosensitive spots, intended to be exposed to light informationcorresponding to the image to be detected, the read circuits associatedwith these photosensitive spots each delivering a measurement voltagerepresentative of the image to be detected, and into blindphotosensitive spots protected from the light information, the readcircuits associated with these blind photosensitive spots eachdelivering a dark voltage serving for temperature compensation. Themethod consists, during detection of an image, in picking up the darkvoltages, then in generating an average correction value from the darkvoltages coming from one or more detected images and in using theaverage correction value to generate a correction voltage from theaverage correction value to be applied, during detection of a subsequentimage, to the read circuits associated with the detecting photosensitivespots so that they deliver a measurement voltage made substantiallyindependent of temperature.

[0028] More particularly, it consists in converting, in ananalog-to-digital converter, the measurement and dark voltages of thephotosensitive spots and in generating the average correction value fromthe digitized dark voltages, this average correction value serving tocontrol a digital-to-analog converter which delivers the correctionvoltage to be applied to the read circuits associated with the detectingphotosensitive spots.

[0029] It is preferable for the average correction value to be generatedby simple averaging over dark voltages coming from several detectedimages.

[0030] Even better results are obtained if the average correction valueis generated by sliding averaging over the dark voltages coming fromseveral detected images.

[0031] To make the compensation even more effective, the averaging willbe compatible with the thermal time constant of the image detector; todo this, the average correction value is generated from dark voltagescoming from one or more detected images, the time interval separatingthe detection of the earliest image from the detection of the mostrecent image used in the averaging being less than the thermal timeconstant of the detector.

[0032] The present invention also relates to a temperature-compensatedimage detector comprising photosensitive spots, each connected to a rowconductor and a column conductor, each photosensitive spot beingconnected via one of its conductors to a read circuit. Thephotosensitive spots are divided into detecting photosensitive spots,intended to be exposed to light information corresponding to the imageto be detected, the read circuits associated with these photosensitivespots each delivering a measurement voltage representative of the imageto be detected, and into blind photosensitive spots protected from thelight information, the read circuits associated with these blindphotosensitive spots each delivering a dark voltage used for temperaturecompensation. It comprises means for picking up the dark voltages duringdetection of an image and for generating an average correction valuefrom the dark voltages picked up coming from one or more detected imagesand means for generating, from the average correction value, acorrection voltage intended to be applied to the read circuitsassociated with the detecting photosensitive spots, during detection ofa subsequent image, so that the detecting photosensitive spots deliver ameasurement voltage made approximately independent of temperature.

[0033] The means for picking up the dark voltages and for generating theaverage correction value receive the dark voltages in digital form fromat least one analog-to-digital converter placed between the readcircuits and the means for generating the average correction value.

[0034] The means for generating the correction voltage comprise adigital-to-analog converter placed between the means for picking up thedark voltages and for generating the average correction value and theread circuits of the detecting photosensitive spots.

[0035] The read circuit associated with a detecting photosensitive spotis a charge-integrating circuit comprising a capacitor, one plate ofwhich receives charges from the detecting photosensitive spot via thecharge conductor and the other plate of which is at the correctionvoltage.

[0036] The read circuit associated with a blind photosensitive spot is acharge-integrating circuit comprising a capacitor, one plate of whichreceives charges from the blind photosensitive spot via the conductorand the other plate of which is at a fixed reference voltage.

[0037] In a simple manner, so as not to degrade the resolution of theimage detector, it is preferable for the blind photosensitive spots tobe connected to an outermost portion of a row conductor.

[0038] The blind photosensitive spots will be covered with a materialopaque to the light information to which the detecting photosensitivespots are exposed, such as black paint.

[0039] When the detecting photosensitive spots are covered with ascintillator material which converts X-radiation into light information,the blind photosensitive spots are covered with an X-ray-opaque materialsuch as lead, the opaque material, when it is present, lies between thelead and the blind photosensitive spots.

[0040] Further features and advantages of the invention will becomeapparent on reading the description which follows, illustrated by thefigures which show:

[0041]FIG. 1, already described, a schematic top view of a known imagedetector;

[0042]FIG. 2a, a top view of an example of an image detector accordingto the invention; and

[0043]FIG. 2b, a sectional view of the image detector in FIG. 2a.

[0044] In these figures, the scales have not been respected for the sakeof clarity.

[0045] Referring to FIGS. 2a, 2 b, the photosensitive spots O1 to O6 andR1 to R9 are shown in the same way as in FIG. 1, with a photodiode Dpand an element having a switch function Dc, shown in the form of aswitching diode. This switching diode could have been replaced with atransistor. The photodiode Dp and the switching diode Dc are connectedtogether in a back-to-back arrangement. Each photosensitive spot isconnected between a row conductor Y1 to Y3 and a column conductor W1, W2and Z1 to Z3. The photosensitive spots O1 to O6 and R1 to R9 arearranged in a matrix of rows and columns. Compared with the example inFIG. 1, the image detector has more photosensitive spots and more columnconductors, but the same number of row conductors. The row conductorsare connected to an addressing device 3 similar to that described inFIG. 1.

[0046] According to one feature of the invention, the photosensitivespots are divided into two categories—detecting photosensitive spots R1to R9, intended to be exposed to light information carrying the image tobe detected, and blind photosensitive spots O1 to O6 used fortemperature compensation. These blind photosensitive spots O1 to O6 aremasked from the light information carrying the image to be detected.During detection of an image, whether this is a useful image or anoffset image, the blind photosensitive spots receive nothing. Theseblind photosensitive spots O1 to O6 will be read in the same way as thedetecting photosensitive spots R1 to R9.

[0047] The blind photosensitive spots O1 to O6 are connected tooutermost portions 20 of the row conductors Y1 to Y3. In the exampledescribed they are located at the start of a row, but they could belocated at the end of a row.

[0048] The number of blind photosensitive spots is not critical—about 10per row seems reasonable if a row numbers about 2000 detectingphotosensitive spots. These photosensitive spots O1 to O6, R1 to R9 areimplanted on an insulating substrate with the reference 21.

[0049] To mask the blind photosensitive spots O1 to O6 from the lightinformation, they are covered with a material PN opaque to the lightinformation—black paint for example is very suitable.

[0050] In the configuration in which the image detector according to theinvention is used in a radiological application, the detectingphotosensitive spots R1 to R9 are covered with a scintillator materialSC which coverts X-radiation into radiation in the band of wavelengthsat which the detecting photosensitive spots R1 to R9 are sensitive. Asregards the blind photosensitive spots O1 to O6, these are not coveredwith the scintillator material SC but with an X-ray-opaque material PB,for example a layer of lead. In this configuration, the material PNopaque to the light information is optional, but if some is used it isplaced between the blind photosensitive spots O1 to O6 and theX-ray-opaque material PB.

[0051] The entire surface of the image detector on that side from whichthe X-radiation comes is covered with a protective material PP based forexample on carbon fibers.

[0052] As in the example in FIG. 1, the read device CL comprises as manyread circuits 30 a, 30 b as there are column conductors W1, W2 and Z1 toZ3 and these read circuits are of the charge-integrating type. Thecircuits 30 a are connected to the conductors W1 and W2 and the circuits30 b to the conductors Z1 to Z3. They receive charges via theseconductors. Each integrating circuit 30 a, 30 b also receives, as input,a fixed input reference voltage VR. Each charge-integrating circuit 30a, 30 b comprises an integration capacitor 31 a, 31 b, one plate ofwhich receives the charges via the conductor W1, W2 and Z1 to Z3 towhich the integrating circuit 30 a, 30 b is connected. These chargescome essentially from the photosensitive spot which is being read. Theother plate of the capacitor 31 a, 31 b is at a potential which will nowbe explained. If there is a read circuit 30 a connected to a conductorW1, W2 leading to a blind photosensitive spot O1 to O6, this voltage isan absolute reference voltage VDR0. If there is a read circuit 30 bconnected to a conductor Z1 to Z3 leading to a detecting photosensitivespot R1 to R9, this voltage is a temperature-slaved correction voltageVDR.

[0053] The voltage Vs2 present at the output 32 b of a read circuit 30 bconnected to a conductor Z1 to Z3 leading to a detecting photosensitivespot R1 to R9 is then given by:

Vs2=VDR−Q/C

[0054] where Q is the amount of charge integrated by the integratingcapacitor 31 b and C is the capacitance of the integrating capacitor 31b.

[0055] The voltage present at the output 32 a of a read circuit 30 a isobtained in a similar manner.

[0056] Each integrating circuit 30 a, 30 b comprises a resetting switchIa, Ib mounted in parallel with the corresponding integrating capacitor31 a, 31 b, respectively.

[0057] The outputs 32 a, 32 b of the read circuits are connected to amultiplexing device 60 which delivers, as a series, signalscorresponding to the charges which were integrated by thecharge-integrating circuits. In the read phase, these signals correspondto the charges accumulated by all the photosensitive spots of the sameline. The signals delivered by the multiplexing device 60 are thendigitized in at least one analog-to-digital converter (ADC) 70. Thedigitized signals are transmitted to a management device 80 which canreceive them, that is to say store, process and, optionally, displaythem.

[0058] During a read phase, the read circuits 30 b associated with thedetecting photosensitive spots R1 to R9 each deliver a measurementvoltage corresponding to the exposure received by the detectingphotosensitive spot, whereas the read circuits 30 a associated with theblind photosensitive spots O1 to O6 each deliver a dark voltage used foreffecting the temperature compensation of the image detector since theblind photosensitive spots have not been exposed.

[0059] During detection of an image, the dark voltages are picked up anddelivered, in digital form as output by the analog-to-digital converter70, to the management device 80. An average correction value is thengenerated in the management device from the dark voltages coming fromone or more detected images. In FIG. 2a, the management device 80,produced with one or more memories and a computing device, is shownseparately from a display device 80.1 which allows the detected imagesto be displayed. It would be conceivable for the two devices to becombined into one.

[0060] There are also means 90 for generating, from the averagecorrection value, the correction voltage VDR to be applied to the readcircuits 30 b associated with the detecting photosensitive spots R1 toR9, during detection of a subsequent image to be compensated. Thesemeans 90 for generating the correction voltage VDR have their inputconnected to the management device 80 and their output to the readcircuits 30 b connected to a conductor leading to detectingphotosensitive spots. These means are shown in the form of adigital-to-analog converter (DAC) 90.

[0061] By applying this correction voltage VDR, the measurement voltagesat the output 32 b of the read circuits 30 b remain substantiallyindependent of temperature.

[0062] To improve the effectiveness of the temperature compensation, itis preferable to generate the average correction value by averaging overa large number of images. It is possible to perform a simple averaging,that is to say all the images used for the averaging are assigned thesame weight. The effectiveness is improved further if sliding averagingis performed, that is to say the earlier images used in the average areassigned a lower weight than the more recent images.

[0063] To further refine the correction, it is preferable to perform anaveraging compatible with the thermal time constant of the imagedetector. For this purpose, the average correction value is generatedfrom dark voltages coming from one or more detected images, the timeinterval separating detection of the earliest image from detection ofthe most recent image used in the averaging being less than the thermaltime constant of the detector.

[0064] This means that if the thermal time constant of the detector isten minutes, the averaging will take place over at most ten minutes.

1. A method for temperature compensation of an image detector comprising photosensitive spots (O1 to O6, R1 to R9), these being sensitive to ambient temperature, each connected to a row conductor (Y1 to Y3) and a column conductor (W1, W2, Z1 to Z3), each of the photosensitive spots being connected via one of its conductors to a read circuit (30 a, 30 b), characterized in that the photosensitive spots are divided into detecting photosensitive spots (R1 to R9), intended to be exposed to light information corresponding to the image to be detected, the read circuits (30 b) associated with these photosensitive spots each delivering a measurement voltage representative of the image to be detected, and into blind photosensitive spots (O1 to O6) protected from the light information, the read circuits (30 a) associated with these blind photosensitive spots each delivering a dark voltage serving for temperature compensation, and in that it consists, during detection of an image, in picking up the dark voltages, then in generating an average correction value from the dark voltages coming from one or more detected images and in using the average correction value to generate a correction voltage (VDR) to be applied, during detection of a subsequent image, to the read circuits (30 b) associated with the detecting photosensitive spots (R1 to R9) so that they deliver a measurement voltage made substantially independent of temperature.
 2. The method for temperature compensation of an image detector as claimed in claim 1, characterized in that it consists in converting, in an analog-to-digital converter (70), the measurement and dark voltages of the photosensitive spots and in generating the average correction value from the digitized dark voltages, this average correction value serving to control a digital-to-analog converter (90) which delivers the correction voltage to be applied to the read circuits associated with the detecting photosensitive spots.
 3. The method for temperature compensation of an image detector as claimed in either of claims 1 and 2, characterized in that it consists in generating the average correction value by a simple averaging over dark voltages coming from several detected images.
 4. The method for temperature compensation of an image detector as claimed in either of claims 1 and 2, characterized in that it consists in generating the average correction value by a sliding averaging over the dark voltages coming from several detected images.
 5. The method for temperature compensation of an image detector as claimed in one of claims 1 to 4, characterized in that it consists in generating the average correction value from dark voltages coming from one or more detected images, the time interval separating the detection of the earliest image from the detection of the most recent image used in the averaging being less than the thermal time constant of the detector.
 6. The method for temperature compensation of an image detector as claimed in one of claims 1 to 5, characterized in that it consists in connecting the blind photosensitive spots to an outermost portion (20) of at least one row conductor (Y1 to Y3).
 7. A temperature-compensated image detector comprising photosensitive spots (O1 to O6, R1 to R9), each connected to a row conductor (Y1 to Y3) and a column conductor (W1, W2, Z1 to Z3), each photosensitive spot being connected via one of its conductors to a read circuit (30 a, 30 b), characterized in that the photosensitive spots are divided into detecting photosensitive spots (R1, R9), intended to be exposed to light information corresponding to the image to be detected, the read circuits (30 b) associated with these photosensitive spots each delivering a measurement voltage representative of the image to be detected, and into blind photosensitive spots (O1 to O6) protected from the light information, the read circuits (30 a) associated with these blind photosensitive spots each delivering a dark voltage used for temperature compensation and in that it comprises means for picking up the dark voltages during detection of an image and for generating an average correction value from the dark voltages picked up coming from one or more detected images and means for generating, from the average correction value, a correction voltage (VDR) intended to be applied to the read circuits (30 b) associated with the detecting photosensitive spots, during detection of a compensated subsequent image, so that the detecting photosensitive spots (R1 to R9) deliver a measurement voltage made approximately independent of temperature.
 8. The temperature-compensated image detector as claimed in claim 7, characterized in that the means (80) for picking up the dark voltages and for generating the average correction value receive the dark voltages in digital form from at least one analog-to-digital converter (70) placed at the output of the read circuits (30 a, 30 b).
 9. The temperature-compensated image detector as claimed in claim 8, characterized in that the means (90) for generating the correction voltage comprise a digital-to-analog converter placed between the means for picking up the dark voltages and for generating the average correction value (80) and the read circuits (30 b) of the detecting photosensitive spots.
 10. The temperature-compensated image detector as claimed in one of claims 7 to 9, characterized in that the read circuit (30 b) associated with a detecting photosensitive spot (R1 to R9) is a charge-integrating circuit comprising a capacitor (31 b), one plate of which receives charges from the detecting photosensitive spot (R1 to R9) via the charge conductor (Z1, Z2, Z3) and the other plate of which is at the correction voltage (VDR).
 11. The temperature-compensated image detector as claimed in one of claims 7 to 10, characterized in that the read circuit (30 a) associated with a blind photosensitive spot (O1 to O6) is a charge-integrating circuit comprising a capacitor (31 a), one plate of which receives charges from the blind photosensitive spot (O1 to O6) via the conductor (W1, W2) and the other plate of which is at a fixed reference voltage (VDR0).
 12. The temperature-compensated image detector as claimed in one of claims 7 to 11, characterized in that the blind photosensitive spots are connected to an outermost portion (20) of a row conductor (Y1 to Y3).
 13. The temperature-compensated image detector as claimed in one of claims 7 to 12, characterized in that the blind photosensitive spots (O1 to O6) are covered with a material (PN) opaque to the light information to which the detecting photosensitive spots are exposed, such as black paint.
 14. The temperature-compensated image detector as claimed in one of claims 7 to 13, characterized in that the detecting photosensitive spots (R1 to R9) are covered with a scintillator material (SC) which converts X-radiation into light radiation and the blind photosensitive spots (O1 to O6) are covered with an X-ray-opaque material (PB) such as lead, the material (PN) opaque to the light information, when it is present, lying between the X-ray-opaque material (PB) and the blind photosensitive spots (O1 to O6). 